This invention relates to growing an extension on an end of an article having a directionally oriented microstructure, and, more particularly, to such a method in which the end is used as a growth seed for the extension and article extended thereby.
The reported technology for growing directionally oriented structures, including single crystals, from a molten bath of a selected material has evolved from simple shapes and members to complex shaped articles. A portion of such technology includes the generation in a complex shaped mold of directionally solidified or single crystal alloy articles for use in the hot sections of gas turbine engines. The published literature well known to those skilled in such art has many examples of articles such as turbine blades and vanes provided in such a manner.
When an article, for example a turbomachinery or gas turbine engine blading member, is operated in an environment of airborne particles and particularly in the strenuous high temperature oxidizing and/or corrosive conditions experienced in the turbine section of a gas turbine engine, oxidation, hot corrosion, erosion, wear, low-cycle fatigue cracking and other damage can occur to such an article. Because the manufacture of such article is expensive, it is desirable economically to repair rather than to replace the article.
An example of a complex shaped blading member of the type referred to above is the turbomachinery blade described in Andersen et al. U.S. Pat. No. 4,010,531 patented Mar. 8, 1977 and assigned to the assignee of this invention. Such a blade includes a complex hollow interior communicating with an open tip for cooling purposes. The disclosure of such patent is hereby incorporated herein by reference.
Through the use of the above referred to reported technology, an article such as a blading member can be manufactured as a single crystal or with a directionally solidified microstructure of elongated grains. The combination of casting mold technology and casting procedures enables such manufacture. As used herein for simplicity, the term "directionally oriented" is intended to include directionally solidified elongated grained structures as well as single crystal structures, the crystal orientation or growth direction of which is maintained in a selected direction. As is well known in the art of blading members, the characteristic crystal orientation in nickel-base superalloys frequently used for blading members is that the &lt;001&gt; crystallographic direction lies substantially parallel to the growth direction; designers of such blading members can utilize that characteristic crystal orientation to minimize the elastic modulus, and therefore reduce the likelihood of mechanical failure due to a mechanism such as thermal fatigue, along a specified direction relative to the configuration of an article such as a blading member.
When such a complex shaped article having a directionally oriented microstructure is damaged, either in operation or in a portion of its manufacturing procedure, the problem of its repair becomes more complicated and difficult. This problem of repair becomes particularly acute when a directionally oriented structure is intended to be maintained in the repaired portion, as is typically desired in directionally oriented articles such as airfoils, for example, blading members.